GRAS 26AC-1 1/4″ Standard Preamplifier with Integrated Miniconnector

Design

All GRAS microphone preamplifiers are based on a small ceramic thick-film substrate with a very high input impedance. The ceramic substrate is shielded by a guard ring to minimize the influence of stray capacitance and microphonic interference. The casing is made of stainless steel for maximum strength and durability. This preamplifier ensures reliable operation even under humid conditions owing to the heat generated by internal power dissipation.

The 26AC-1 is delivered with a built-in TEDS chip, and can be programmed as a single unit with a microphone fitted. An adaptor (GRAS GR0010) for GRAS 1/2″ microphone cartridges is included.

Dynamic Range

GRAS 26AC-1 can handle both single and dual-sided power supplies. The supply can vary between 28 VDC and 120 VDC single-sided or ±14 VDC and ±60 VDC dual-sided. When using the high supply voltage (120 VDC or ±60 VDC), the dynamic range exceeds 140 dB. 

Noise

The electrical circuit in GRAS 26AC-1 is built on a ceramic substrate using selected low-noise components to gain very low self-noise. The electrical self-noise is so low that system noise is mainly determined by the microphone cartridge’s thermal noise.

Frequency response

The low-frequency cut-off of the GRAS 26AC-1 preamplifier is mainly determined by the input impedance of the preamplifier and the capacitance of the microphone cartridge (see the graph in the Specifications). The capacities 20 pF,6.5 pF and 3 pF equal the typical capacitances of 1/2″, 1/4″” and 1/8″ microphone cartridges respectively. The high-frequency cut-off is determined by the preamplifier’s ability to drive capacitive loads (slew rate), caused by the cable. For large-signals, the effects of these parameters must be accounted for when measurements are performed. A graph in the Specifications shows the large-signal response for GRAS 26AC-1 for various capacitive loads corresponding to different cable lengths. The output level is in decibels relative to 1 Volt. Typical capacitance for the cable is 100pF/m (30pF/foot).

Connector

The GRAS 26AC-1 1/4″ Preamplifier is provided with a 5-pin LEMO series integrated connector. Cables for conversion to standard 7-pin LEMO series 1B plug are available.

5-pin LEMO plug 00 male (ext. view)

Typical applications and use

General-purpose preamplifier

High-frequency measurements

High-pressure measurements